This is rhyming slang.
Dame Judi Dench = stench.
It naturally is no reflection on the actress or her thespian abilities. The joy of the phrase is the total irrelevance of the subject to the meaning.

It is quoted several times in Irvine Welsh's novels; some readers have misunderstood what it means when used in phrases liked "He left a Dame Judi Dench in the toilet" - the text would refer to the odour, not the stool.

1. Who made that awful Dame Judi?
2. The toilet was filled with a terrible Judi Dench.